Alzheimer's disease is a progressive illness that kills neurons in the brain, initially causing memory loss and eventually leading to dementia. It afflicts some four million older adults in the United States, and perhaps three times as many individuals suffer early-stage forms of the disease that incapacitate memory to one degree or another. Currently, the disease can be diagnosed definitely only after a person dies by an autopsy that shows certain brain abnormalities.
As recognized by the present inventors, brain researchers would like to reliably identify changes in brain structure and metabolism associated with early Alzheimer's disease, before symptoms emerge. Such information would buy precious time when potential therapies could delay or prevent the memory-robbing disease altogether. Furthermore, where the onset of Alzheimer's disease has already been determined, it is of great interest to be able to measure the progression rate of brain atrophy, as recognized by the present inventors.
Research by the present inventors and others have shown that magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging can reveal structural and metabolic changes in the brain that appear to point to early losses in memory and intellectual ability. For example, the present inventors have demonstrated with MRI scans that the hippocampus of the brain shrinks in people with mild cognitive impairment (MCI), a form of memory loss that often precedes Alzheimer's.
Despite the promise of the MRI studies, the hippocampus of the brain is notoriously difficult to measure due to its sea horse shape and its size (typically only four centimeters long). The entorhinal cortex of the brain is even smaller than the hippocampus, and it too is hard to discern reliably. Further, measurements should be made non-invasively to prevent interference with the normal operation of the brain. Similar issues are encountered when changes in the size and/or shape of other organs within the body are determined across a period of time.
As recognized by the present inventors, what is needed is a non-invasive means to measure the change in size of an object or portion of an object, such as an organ or segment of an organ (i.e., structure of the brain, chamber of a heart, and so forth). It is against this background that embodiment of the present invention were developed.